It is well known that the electricity network is not a channel for static communication, or put another way, frequency response, attenuation and noise on the line vary in time, so that a configuration of gain in the transmission and reception amplifiers may be adequate at a given moment, only to become inadequate a few moments later due to a change produced by the behaviour of the network.
On the other hand, users in a communication system over the electricity network see a different channel depending on their position in relation to the head-end, so that a fixed configuration cannot be used for gains in the corresponding amplifiers when the user is connected to the system.
The electricity network behaves as a selective communications channel (being able to attenuate some carriers more than 80 dB with respect to others, or to put it another way, to have a dynamic margin greater than 80 dB). Line noise is also variable (that is, the same noise power is not always measured in reception) and various impulse noises are present. Therefore, conventional systems of automatic gain control are not adequate to be applied to a communication system over the electricity network, where it is necessary to undertake intelligent gain control.
A relevant background art can be found in document WO94/03002, which discloses a system utilizing adaptive frequency-hopped spread spectrum modulation to communicate over noisy communications channels is described. Individual packets of data are transmitted with FSK modulation using two frequencies chosen from a larger set. An error coding system is used in which data on the quality of reception at each network transceiver is used to alter the gain of the receiver, the bit rate of the transmission, and the specific frequencies employed by the network for the purpose of optimizing communication in error rate. A Master transceiver, controlling network management, transmits channel control information to other transceivers on the network, enabling system synchronization, acquisition of an existing network by new subscribers. Each transceiver comprises a frequency controlled carrier generator, a pair of digital detectors each having a frequency controlled bandpass filter microprocessors for control and broad band coupling networks for coupling the transceiver to a communications channel.